In the conventional drilling of a well, such as an oil well, a series of casings and/or liners are commonly installed sequentially in the wellbore or borehole. In standard practice, each succeeding liner placed in the wellbore has an outside diameter significantly reduced in size when compared to the casing or liner previously installed. Commonly, after the installation of each casing or liner, cement slurry is pumped downhole and back up into the space or annulus between the casing or liner and the wall of the wellbore, in an amount sufficient to fill the space. The cement slurry, upon setting, stabilizes the casing or liner in the wellbore, prevents fluid exchange between or among formation layers through which the wellbore passes, and prevents gas from rising up the wellbore.
The use of a series of liners which have sequentially reduced diameters is derived from long experience and is aimed at avoiding problems at the time of insertion of casing or liner installation in the wellbore. The number of liners or casings required to reach a given target location is determined principally by the properties of the formations penetrated and by the pressures of the fluids contained in the formations. If the driller encounters an extended series of high pressure/low pressure configurations, the number of liners required under such circumstances may be such that the well cannot usefully be completed because of the continued reduction of the liner diameters required. Again, a further problem of the standard well liner configuration is that large volumes of cuttings are produced initially, and heavy logistics are required during early phases of drilling.
While several approaches to the resolution of these problems have been attempted, none have proven totally satisfactory. Accordingly, there has existed a need for a well lining and cementing technique or procedure, and means to carry it out, which would eliminate or significantly reduce the degree of diameter reduction required when a series of well liners must be inserted. The invention addresses this need.